Method of manufacturing optical, aspherical correction elements



35M 5R gg-gugg tmmgwyg V mama mu KR 297899318 v tf f) Kw J X p 23, 1957 J. H. J. VAN DIJK EIAL 2,789,318 w I METHOD OF MANUFACTURING OPTICAL, ASPHERICAL 1: CORRECTION ELEMENTS Filed Nov. 7, 1951 Age t I United States Patent METHOD OF MANUFACTURING OPTICAL, ASPHERICAL CORRECTION ELEMENTS Johannes Henrieus Joseph van Dijk, Eindhoven, Antonius Hendricus Hoefkens, Rotterdam, and Felix Robert Schepman, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application November 7, 1951, Serial No. 255,306

Claims priority, application Netherlands November 13, 1950 3 Claims. (Cl. 18-59) It is known to manufacture optical aspherical correction elements by casting a solution of a gelatinisable substance on a solid substratum in an aspherical templet, causing the solution to become a gel by removing the templet and subsequently drying the gel. During the drying operation the gel shrinks substantially only in a direction at right angles to the substratum, so that a resultant thin aspherical element remains on the substratum. For the substratum, use is generally made of a piano-parallel glass plate, on which the element remains permanently fixed.

This method may have a limitation in that the element partly loosens itself from the substratum, more particularly at the edge owing to strain in the gel during the drying operation.

A further limitation is experienced, when the element is removed from the substratum and wanted for separate use. It is then difficult to mount the element in an exactly plane position.

The object of the invention is inter alia to obviate one or both of these two limitations.

According to the invention, the element is provided with an edge prior to its removal from the substratum, if required, and irrespective of the manufacture of the element, this edge being mechanically stronger than that of the element itself. This may, for example, be achieved by choosing the edge to be thicker than the element or by using a stronger material, for example, metal. Consequently, it is not meant to form an edge on the element in one operation with the manufacture of the element itself.

In a preferred embodiment of the invention, the flange is applied in the form of a rim to the substratum prior to the application of the element. This application may be carried out in a particularly simple manner by immersing the edge of the substratum in a solution of the material of which the flange is made.

In a further preferred form, in which the element is removed from the substratum, the flange is fixed to the element, prior to the removal of the latter, for example by sticking it thereon. In this case it is advisable to make the flange of metal or other strong material.

In a further form, the edge of the element is cast around a ring which is made of stronger material and which forms the reinforcing flange.

In order that the invention may be readily carried into effect, a number of examples will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1 is a sketch of a device for applying a stiffening flange in a perspective view;

Fig. 1 is a cross sectional view taken on the axis of a substratum having a stiffening edge;

Fig. 3 is a cross-sectional view of a device for constructing the aspherical element;

2,789,318 Patented Apr. 23, 1957 "ice Figs. 4 and 5 are cross-section views taken on the axis of the element in further stages of manufacture;

Fig. 6 is a cross-sectional view taken on the axis of an element having a substratum in a further embodiment;

Fig. 7 is a side view of a substratum having a ring constituting the stiffening flange;

Fig. 8 shows the gelatinized liquid cast around this ring, also in a side view and Fig. 9 is a cross-sectional view of the finished element.

For the substratum, use will generally be made of a piece of circular mirror glass 1, which has the advantage of being strong, well polished and not expensive. To this substratum is applied a stiffening flange by plunging the glass, while turning it round, with its edge into a solution 2 of a substance which remains in a strong consistent layer after the solvent has evaporated. For this purpose use may, for example, be made of a solution of cellulose-acetate-butyrate in a mixture of acetone and ethylacetate. Further suitable solutions are: a solution of a copolymeride of vinylchloride and vinylacetate (known under the registered trade name of Vinylite VMC in acetone or a solution of polyvinylbutyrate (known under the registered trade name of Butvar) in acetone.

After the solution has been dried, a rim 3 has formed itself (Fig. 2) which may derive its strength from the satisfactory adhesion to the glass, or from the choice of the material, or from the fact that it embraces the glass substratum, or else from the combination of these factors. The substratum is introduced into a recipient 4 (Fig. 3), over which a templet 5 is arranged. This templet has, on its lower side, an aspherical shape and is arranged to be internally heated to any desired temperature by means of a liquid. This liquid may be caused to circulate through the pipes 6.

Through the aperture 7, a warm solution of a gelatinisable substance, for example, a solution of 10% of gelatine in water or a solution of 20% of cellulose-acetatebutyrate in a mixture of xylene and isopropylalcohol is cast into the templet. During the casting operation the templet 5 is heated, but then the templet is cooled, for example, by means of cold water, so that the liquid 8 changes into a gel. A further suitable substance is cellulose-acetate-propionate. In a manner not shown, the substratum is now lifted out of the recipient 4 and the gel is dried. During the drying operation the produced layer 9 (Fig. 4), which now constitutes the optical element, adheres excellently to the rim 3. A further stiffening rim 10 may, moreover, be arranged about the flange and the element 9 in the same manner as that in which the rim 3 was formed (Fig. l).

The element may now be arranged in an optical system, for example in the known Schmidt mirror system. It may then remain fixed to the glass substratum, but it may, as an alternative, be removed therefrom, for example, by cutting the rim 3 and 10 on the arrows 11 of Fig. 4 and by removing the element 9 from the glass. The disengagement of the element may be furthered by plunging it into water or by greasing the glass very slightly. If the element is made of gelatin, it must, of course, be previously hardened, which may be carried out with the use of formalin. The element thus obtained is shown in Fig. 5.

In the case described above, the stiffening rim 3 is arranged around the edge of the glass 1.

In certain cases, it may be supposed to be suflicient to provide a flange 3 only on one side of the glass, for example when the substance of which the element is made adheres in a poor manner to the glass. The stiffening flange 3 may then be made of a material which adheres excellently to the glass and to which the material of the element also adheres well. The stiffening flange will then prevent the element from bursting off.

According to a further embodiment, the element 9 (Fig. 6) is provided with a strong flange, for example in the form of a metal ring 12, by adhesion with the use of an adhesive 13. Such an element is particularly suitable for separate use in an optical system, after having been removed from the substratum.

A further suitable method consists in that a metal ring is provided at a short distance over the substratum 1 (Fig. 7). This ring may, for example, be supported at three points (15). Then the gelatinisable solution 8 is cast on the substratum and caused to form a gel (Fig. 8). This gel is then dried in the manner described above. If the supports 15 of the ring 14 cannot follow the shrinkage, a small deformation of the element will occur at the edge. However, this deformation is located outside the optically effective part of the element. As a matter of course, the supports may, as an alternative, be provided temporarily and removed subsequent to the gelatinisation of the liquid.

Subsequently to the drying operation (Fig. 9) a small elevation 16 will be shown at the area of the ring 14.

Since, in all these cases, the stiffening flange is provided prior to the removal of the element from the substratum, it is substantially certain that the element obtained will keep its correct shape, i. e. the surface which first engaged the glass remains completely smooth.

With the choice of the material of the stiffening flange the expansion coefficient must, of course, be taken into consideration. In general, it must not deviate considerably from that of which the element itself is made.

What we claim is:

l. A method of manufacturing an optical, aspherical correction element comprising the steps of immersing a substratum in a solution of a substance which remains as a U-shaped stiffening flange on the circumferential edge of said substratum after the solvent has evaporated, placing said substratum in a receptacle, arranging an aspherical templet in said receptacle over said substratum, intro ducing a solution of a gelatinisable substance between said templet and said substratum, and removing said templet and drying the resulting gel, said resulting gel adhering to said U-shaped stiffening flange during said drying operation.

2. A method of manufacturing an optical, aspherical correction element comprising the steps of immersing the edge portions of a substratum into a solution of a substance thus forming a U-shaped stiffening ring on said substratum after said ring has dried, placing said substratum in a receptacle, arranging an aspherical templet in said receptacle over said substratum, introducing a. solution of a gelatinisable substance between said templet and said substratum, and removing said templet and drying the resulting gel.

3. A method of manufacturing an optical, aspherical correction element comprising the steps of immersing a substratum in a solution of a substance which remains as a first stiffening flange of U-shaped cross-section on said substratum after the solvent has evaporated, placing said substratum in a receptacle, arranging an asphcrical templet in said receptacle over said substratum, introducing a solution of a gelatinisable substance between said templet and said substratum, removing said templet, drying the resulting gel, removing said element from said substratum, said element adhering to said U-shaped flange, and immersing said element in a solution of a substance which remains as a second stiffening flange of U-shaped cross-section around both the circumferential edge of said substratum and said first stiffening flange.

References Cited in the file of this patent UNITED STATES PATENTS 869,311 Leuchter Oct. 29, 1907 1,297,660 Collins Mar. 18, 1919 1,721,194 Tillyer July 16, 1929 2,330,663 Bennett et a1. Sept. 28, 1943 2,332,930 Rinia Oct. 26, 1943 2,437,860 Rinia Mar. 16, 1948 2,510,521 Rinia June 6, 1950 2,530,742 Van Alphen Nov. 21, 1950 2,543,778 Henroteau Mar. 6, 1951 2,635,289 Owens Apr. 21, 1953 FOREIGN PATENTS 490,381 Great Britain Aug. 15, 1938 

